In prokaryotic and eukaryotic cells, the 39-59-exonucleolytic decay and processing of RNAs are essential for RNA metabolism. However, the understanding of the mechanism of 39-59-exonucleolytic decay in plants is very limited. Here, we report the characterization of an Arabidopsis (Arabidopsis thaliana) transfer DNA insertional mutant that shows severe growth defects in early seedling growth, including delayed germination and cotyledon expansion, thinner yellow/pale-green leaves, and a slower growth rate. High-efficiency thermal asymmetric interlaced polymerase chain reaction analysis showed that the insertional locus was in the sixth exon of AT4G27490, encoding a predicted 39-59-exonuclease, that contained a conserved RNase phosphorolytic domain with high similarity to RRP41, designated RRP41L. Interestingly, we detected highly accumulated messenger RNAs (mRNAs) that encode seed storage protein and abscisic acid (ABA) biosynthesis and signaling pathway-related protein during the early growth stage in rrp41l mutants. The mRNA decay kinetics analysis for seed storage proteins, 9-cis-epoxycarotenoid dioxygenases, and ABA INSENSITIVEs revealed that RRP41L catalyzed the decay of these mRNAs in the cytoplasm. Consistent with these results, the rrp41l mutant was more sensitive to ABA in germination and root growth than wild-type plants, whereas overexpression lines of RRP41L were more resistant to ABA in germination and root growth than wild-type plants. RRP41L was localized to both the cytoplasm and nucleus, and RRP41L was preferentially expressed in seedlings. Altogether, our results showed that RRP41L plays an important role in seed germination and early seedling growth by mediating specific cytoplasmic mRNA decay in Arabidopsis.

Leaf senescence is the final stage of leaf life history, and it can be regulated by multiple internal and external cues. La-related proteins (LARPs), which contain a well-conserved La motif (LAM) domain and normally a canonical RNA recognition motif (RRM) or noncanonical RRM-like motif, are widely present in eukaryotes. Six LARP genes (LARP1a-1c and LARP6a-6c) are present in Arabidopsis, but their biological functions have not been studied previously. In this study, we investigated the biological roles of LARP1c from the LARP1 family. Constitutive or inducible overexpression of LARP1c caused premature leaf senescence. Expression levels of several senescence-associated genes and defense-related genes were elevated upon overexpression of LARP1c. The LARP1c null mutant 1c-1 impaired ABA-, SA-, and MeJA-induced leaf senescence in detached leaves. Gene expression profiles of LARP1c showed age-dependent expression in rosette leaves. Taken together, our results suggest LARP1c is involved in regulation of leaf senescence.

The 4SN-Tudor domain protein is an almost ubiquitous eukaryotic protein with four Staphylococcal nuclease domains at the N terminus and a Tudor domain towards the C terminus. It has been found that Tudor-SN protein has multiple roles in governing gene expression during cell growth and development in animals. In plant, although Tudor-SN orthologs have been found in rice, pea and Arabidopsis, and are associated with cytoskeleton, their roles in growth and development are poorly understood. In this study, we investigated the function of Arabidopsis Tudor-SN protein, AtTudor. Our results indicated that the expression of AtTudor2 in seeds was evidently higher than in other tissues. Furthermore, we found that the expression of a key enzyme for GA biosynthesis, AtGA20ox3, was downregulated obviously in AtTudor2 T-DNA insertion mutant and AtTudor1/AtTudor2 RNAi transgenic lines. Together, our results suggest that AtTudor2 is involved in GA biosynthesis and seed germination of Arabidopsis.

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